Solar cells are known in the art. A solar cell may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrate. These layers may be supported by a glass substrate. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
Substrate(s) in a solar cell are sometimes made of glass. Glass that is fairly clear in color and highly transmissive to visible light is sometimes desirable. Glass raw materials (e.g., silica sand, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron, which is a colorant. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the from of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. While iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color since iron in the ferric state tends to be weaker as a colorant than its ferrous state counterpart.
It has been found that the use of a low-iron highly transparent patterned glass is advantageous for solar cell applications. The use of the low-iron composition in combination with the patterned surface(s) of the glass substrate(s) has been found to be advantageous with respect to optical properties, thereby leading to increased solar efficiency of a solar cell.
In certain example embodiments of this invention, a solar cell patterned glass substrate has a visible transmission of at least 75% (more preferably at least 80%, even more preferably at least 85%, and most preferably at least about 90%). In making such a glass, a batch therefor includes a base glass (e.g., soda lime silica glass) and in addition comprises (or consists essentially of in certain other embodiments) a very small amount of total iron.
Optionally, an amount of cerium oxide may also be present. In certain example embodiments, the patterned glass substrate may have fairly clear color that may be slightly yellowish (a positive b* value is indicative of yellowish color). For example, in certain example embodiments, the patterned glass substrate may be characterized by a visible transmission of at least 90%, a total solar/energy value of at least 90%, a transmissive a* color value of from −1.0 to +1.0 (more preferably from −0.5 to +0.5, and most preferably from −0.2 to 0), and a transmissive b* color value of from 0 to +1.5 (more preferably from +0.1 to +1.0, and most preferably from +0.2 to +0.7). These properties may be realized at an example non-limiting reference glass thickness of from about 3-4 mm.
In certain example embodiments of this invention, there is provided a solar cell comprising: a patterned glass substrate, wherein at least one surface of the patterned glass substrate has a surface roughness of from about 0.1 to 1.5 μm; first and second conductive layers with at least a photoelectric film provided therebetween; wherein the glass substrate is of a composition comprising:
Ingredientwt. %SiO267-75%Na2O10-20%CaO 5-15%total iron (expressed as Fe2O3)0.001 to 0.06% cerium oxide  0 to 0.30%wherein the glass substrate has visible transmission of at least 90%, a transmissive a* color value of −1.0 to +1.0 and a transmissive b* color value of from 0 to +1.5. The amount of total iron oxide (expressed as Fe2O3) is more preferably from 0.02 to 0.06%. MgO may also be provided in the glass in certain example embodiments.
In other example embodiments of this invention, there is provided a method of making patterned glass, the method comprising: providing a molten glass batch in a furnace or melter comprising from 67-75% SiO2, from about 0.001 to 0.06% (more preferably from 0.01 to 0.06%) total iron, and from about 0 to 0.30% cerium oxide; providing the glass batch so as to have a batch redox of at least 10; forwarding a glass ribbon from the furnace or melter to a nip between first and second rollers, at least one of the rollers having patter defined in a surface thereof, wherein the glass ribbon reaches the nip at a temperature of from about 1,900 to 2,400 degrees F.; at the nip, transferring the pattern from the roller(s) to the glass ribbon; the glass ribbon being at a temperature of from about 1,100 to 1,600 degrees F. upon exiting the nip; annealing the glass ribbon at least after the ribbon exits the nip, thereby providing a patterned glass having a visible transmission of at least 90%, from about 0.001 to 0.06% (more preferably from 0.01 to 0.06%) total iron, and from about 0 to 0.30% cerium oxide.
In certain example embodiments of this invention, the glass has no more than 0.07% cerium oxide, more preferably no more than 0.06%, a transmissive a* color value of −0.5 to +0.5 and a transmissive b* color value of from +0.1 to +1.0.